1. Field of the Invention
The present invention relates generally to the use of a novel vaccine to treat and novel assays to diagnose a host of hemoflagellate protozoal infections, including infections arising from a variety of African trypanosomes.
2. Description of the Related Art
The World Health Organization estimates that at least 37 million people are afflicted annually with a hemoflagellate protozoal infection, some fatally. As many, if not more, domestic protein producing animals are also similarly afflicted. A vaccine has not been produced prior to now because (1) the parasite's ability to change it's surface coat, in the case of African trypanosomes, (2) the ability to induce immunosuppression in all trypanosomes and Leishmania, and (3) the ability of the parasite to hide intracellularly at some point in the infection. Previously, in African trypanosomes, the only immunity that could be obtained was to a single isolate from a single strain. This immunity was ineffective against any other isolate from the same strain or any other strain or species of African trypanosomes.
Olenick et al., Infect. Immun., 56: 92 (1988), report that a mixture of proteins of approximately 80, 74, 40 and 25 kDa, originally derived from the flagellar pocket of Trypanosoma brucei rhodesiense gives protection across variants of Trypanosoma brucei rhodesiense. However, it is unclear from Olenick et al. whether the antigens are common to all African trypanosomes or, indeed, to all hemoflagellate protozoa. In this regard, the mere fact that Olenick et al. achieved immunoprotection across variants of Trypanosoma brucei rhodesiense does not alone suggest that the antigens involved are common to other species of African trypanosomes or to other hemoflagellate protozoa.
Possibly, a similar protein gives immunoprotection across species of African trypanosomes. See, Powell, Med. J. Zambia, 10: 32 (1976); Powell et al., Med. J. Zambia, 12: 67 (1978); and Powell, Experientia, 34: 1450 (1978). Ruiz et al., Immunol. Lett., 12: 1 (1986), report the flagellar antigens in Trypanosoma cruzi to be immunoprotective against Trypanosoma cruzi, but antibodies to this antigen also give antibodies to mammalian cardiac tissue (see U.S. Pat. No. 4,298,590). This flagellar pocket site on the parasite, in African trypanosomes, is also reported to be involved in receptor-mediated endocytosis. See, Coppens et al., Proc. Natl. Acad. Sci. USA, 85: 6753 (1988); Webster, Eur. J. Cell Biol., 49: 295 (1989); and Webster et al., Eur. J. Cell Biol., 49: 303 (1989).
Published patent application WO 92/22325 teaches that a unique protein antigen originally derived from Trypanosoma brucei rhodesiense organisms can be used to induce immunoprotection against all African trypanosomes, Trypanosoma cruzi, all species of Leishmania, and other parasitic hemoflagellate protozoa. However, sequence and other data that would facilitate the preparation of the antigen by recombinant means are not disclosed. Preparation by recombinant means is necessary to produce the vaccine in sufficient quantities to meet current needs and in a cost effective manner.